1. Field of the Invention
This invention relates to mine vehicles and particularly relates to such vehicles having a rotary boring tool, a rectilinear elevation means for the boring tool, and a power means which is the source of energy for imparting torque to the boring tool, movement to the elevation means, and travel to the vehicle. It especially relates to sealing means for excluding contaminants from the boring tool, to bearing means for maintaining its stationary and rotating parts in alignment, and to lubricating means for the sealing means and bearing means.
2. Review of the Prior Art
Tunnelling and continuous mining involve considerable hazards to operators from falling rock. Nearly one-half of the fatal injuries received in coal mining in the United States are caused by roof falls, particularly where blasting is involved in tunnel mining beneath thin limestone, shale, or sandstone strata.
As a protective measure, it has become standard practice to install roofing bolts, spaced apart at selected distances, perpendicularly into the strata in order to bind them together and prevent delamination and sequential collapse of a stratified roof.
Such roofing bolts may be up to seven feet in length and weigh twenty pounds or more. They are inserted by the operator into a hole which he has bored into the mine roof with a roof-bolting machine until he senses that hard strata is being encountered. The bolt is made of soft iron and in low-roof mines is supplied to the operator in a curved shape with a plate of oak or steel at its head. The operator pushes and straightens the bolt until he can use the roof-bolting machine to thrust it securely into place and then to tighten or torque the bolt with a selected force, such as 150 foot-pounds.
In present-day coal mining, about one bolt out of four is a resin bolt which is formed by loading three bags of epoxy components into the bored hole before the bolt is inserted. Turning the bolt breaks the bags and mixes their contents during a forty-second interval before hardening occurs. The resinous material tends to drip down upon the rotary drill head therebeneath, causing damage thereto.
In any of these operations, the operator is exposed to danger from falling rock because he has to work under unsupported roof shortly after blasting operations. He is therefore working under pressure to shore up the roof with oak logs along the edges of a newly blasted portion of the tunnel and then to bolt the roof at required space intervals (such as four feet apart on centers) as soon as possible.
The mine floor is generally wet and more or less covered with a mucky mixture of coal dust and water. Water additionally drips from the roof of the mine. The drill head of the roof bolter generally is provided with a dust collection means, such as that described in U.S. Pat. No. 3,319,727 of Harry G. Pyles, so that its internal rotating machinery is subject to invasion by dust particles from the dust collecting path. In addition, invasion by water from overhead drippings and by wet coal dust, when the drill head is even momentarily lowered to the floor of the mine, is constantly likely. Even slight contamination of the oil which lubricates the drill head is sufficient to wear its seals completely out. The lubricating oil is then sucked into the dust collecting apparatus, often causing plugging thereof. The drill head quickly runs dry, causing the life of a rotary drill head or drill pot typically to be 6-18 months of active service.
This situation is indeed intensified by the confined, dirty, and dangerous working conditions which tend to cause the operators to be oblivious to long-term maintenance responsibilities. It is therefore essential that a sealing means be provided in a drill head whereby the most hasty and even careless operation of the roof bolting machine will not enable dirt to enter its lubricating system from the dust collection system at the center of the drill head, from its upper periphery, or from its bottom when placed on a wet and mucky mine floor.
Such a sealing means is available in the vehicular machine art but has heretofore not been used in the drill head of a roof bolter. It is the sliding mechanical seal which comprises a pair of steel seal rings having circumferentially sliding lapped mating surfaces, each steel ring being compressed by a toric or elastomeric ring which seals an annular space between the respective ring and either a stationary or a rotating member of the machine. This seal is described in U.S. Pat. No. 4,077,634 and in earlier patents such as U.S. Pat. Nos. 3,524,654 and 3,403,916. Commercial products of this type are sold, for example, under the trademark, Duo-Cone, by Caterpillar Tractor Company, Peoria, Illinois, and under the trademark, DF Heavy Duty Seal, by Chicago Rawhide Manufacturing Company, 2720 N. Greenview Avenue, Chicago, Illinois.
However, these seals are built for operation in a vertical or at least an inclined plane so that they rotate partially within a bath of lubricating oil. Moreover, it is not possible to fill the head of a roof bolter to its capacity because the fluid expands 10% when hot. For use within the drill head of a roof bolter, sliding mechanical seals must operate in a horizontal plane between portions of its stationary and rotating assemblies. Accordingly, an overhead lubricating means is needed that will reach and lubricate a sliding mechanical seal and also lubricate the uppermost bearings of the bearing assembly and pinion of the drive assembly within the drill head.
Another problem that has plagued roof bolters of the prior art is bearing failure caused by side thrust at the upper part of the drill head. The side thrust creates sufficient wear of the upper bearings that the entire vertical thrust is then placed upon a few of the bottom bearings so that their life is relatively short. For example, as little as two-thousandths of an inch of wear can cause substantially all vertical thrust to be exerted against only two or three of the bottom thrust bearings. Such side thrust is believed to be at least partially created by the unbalanced rotary thrust from a single hydraulic motor. Accordingly, a means for imparting a balanced rotary thrust is needed.
Such side thrust is also believed to be created by pivotal forces that develop when drilling into inclined strata or when the bit meets an embedded boulder of flint along one side of the borehole. It is further believed that the bearing assemblies of prior art roof bolters have insufficient span between their upper and lower bearings so that the leverage that is developed by these pivotal forces tends to become tremendous and overwhelms their inadequate bearing capacity. A bearing assembly having adequate vertical span and bearing means for resisting the side thrusts developed by pivotal forces is therefore essential.
A third problem that has troubled roof bolters of the prior art is bit breakage when operating in hard roof conditions, such as in sandstone strata. A cause thereof is believed to be insufficient mass in rotary motion. For example, the drill head of one widely used roof bolter weighs no more than about 50 pounds. Such a low mass creates inadequate momentum when the bit contacts a hard spot in the mine roof, thereby forcing the rotary drill head to pause and then to transfer accumulated momentum to the steel bit and its extensions, whereby excessive torsional stresses are created. A means for preventing such accumulation of momentum at rotational speeds up to about 500 rpm is accordingly needed.
A fourth problem of a simple but practical nature that has impeded the operations of prior art roof bolters is the difficulty of opening up and clearing their dust collection system within the drill head when it is clogged by dust mixed with moisture or oil. A simple and rapid means for opening up and forcibly clearing these passages is accordingly needed, one that is dependably available in the dim light of a coal mine even when an operator is tired, in a hurry, and kneeling in a pool of muddy water.
A fifth problem involves protecting the operator from falling rock and guiding the drill steel while drilling. Finding an efficient and compact means for solving this two-sided problem has long plagued the designers of roof bolting machines because it involves the combination of a rotary drill head with an automatically operating roof support, which will rise synchronously with the drill head in order to furnish protection to the operator from falling rock, and with a guide means to keep the drill steel in line while drilling. The crux of this problem is the means and location for attaching the roof support assembly to the frame of the roof bolter.
A sixth problem which has much importance for operators of roof bolting machines is emergency stoppage of the roof bolter at any time, for any reason, and from a variety of operating positions while it is being operated in a mine. Prior art machines are equipped with such emergency devices, but they lack an emergency stopping means that can enable the operator to stop the entire electrical and hydraulic systems of the roof bolter by a single reflex motion without looking at the controls, indeed even in total darkness, from any position along two adjacent sides of the machine, and within lunging distance thereof.